It is well known that chlorine dioxide gas is a strong oxidant, and its oxidizing action is effective in sterilization and decomposition of malodorous substances. Therefore, chlorine dioxide has been used in disinfectant, deodorant and the like. Chlorine dioxide is dissolved in water in 20 times its volume of water, to give a brownish yellow aqueous solution. From the viewpoint of easiness in handling, it is desirable to use chlorine dioxide in a form of such an aqueous solution. However, when the aqueous solution of chlorine dioxide is brought into contact with air, chlorine dioxide gas is rapidly generated. Therefore, there has been proposed a technique in which chlorine dioxide gas is constantly generated while maintaining its stability, by dissolving chlorine dioxide gas in an aqueous solution of sodium peroxycarbonate (Na2C2O6), and thus by forming an aqueous solution containing sodium chlorite (NaClO2) as a main component at a retained pH of 9, i.e., what is called a stabilized aqueous solution of chlorine dioxide (see Patent Document 1).
However, since the stabilized aqueous solution of chlorine dioxide is retained at pH 9 (alkali) for the purpose of maintaining stability, sodium chlorite is dissociated in the aqueous solution as represented by the following equation (1):NaClO2→Na++ClO2−  (1)
Therefore, a generation amount of free chlorine dioxide gas having disinfecting and deodorizing effects or the like is extremely low, and thus it is difficult to attain satisfactory disinfecting and deodorizing effects or the like.
Therefore, it has been proposed that, immediately before its use, a stimulant is added to the stabilized aqueous solution of chlorine dioxide, or an acid is added to lower the pH to 7 or less, for generating chlorine dioxide gas. However, with this technique there arise economical problems that equipments or facilities to implement the processes are required.
In addition, when a stimulant or acid is added in advance to the stabilized aqueous solution of chlorine dioxide, the concentration of the generated chlorine dioxide gas and the retention of the generation depend solely on the concentration of the stabilized aqueous solution of chlorine dioxide, and therefore there is a problem that the concentration of the generated chlorine dioxide gas and the retention of the generation cannot be controlled for the intended use. There is also a problem that chlorine dioxide gas cannot be effectively used for simple disinfection and deodorization of inside of a room, automobile, refrigelator or the like, even though it is effectively used for a large-scale deodorizing treatment of waste gas, organic waste substance and the like generated at business institutions, such as factories.
There has been also proposed a technique in which the stabilized aqueous solution of chlorine dioxide is gelatinized with a gellant, such as agar, gelatine, high water-absorbent resin and the like, to form a gel-like composition. However, with this gel-like composition, the amount of chlorine dioxide gas generation is extremely small, and there is a problem that disinfecting and deodorizing action and the like cannot be satisfactorily obtained.
In order to solve the above-mentioned problems, there has been proposed a technique in which a mixture prepared by adding an organic acid, such as citric acid, to chlorite is blended with a dissolved chlorine dioxide solution, to thereby maintain a chlorine dioxide concentration nearly constant for a long term (see Patent Document 2).    Patent Document 1: Japanese Patent Application JP61-181532A    Patent Document 2: Japanese Patent JP3110724B